Many famous events have occurred within its walls, including the funeral Mass of Charles Carroll of Carrollton, the only Catholic signatory of the Declaration of Independence. Carroll had been the last of the surviving signers. Most of the first American bishops were consecrated here to fill the ever-multiplying dioceses necessitated by the young country's territorial expansion and great waves of immigration. Until recent years, more priests were ordained at the Baltimore Basilica than in any other church in the United States.

The Cathedral is a monumental neoclassical-style building designed in conformity to a Latin crossbasilica plan — a departure on Latrobe's part from previous American church architecture, but in keeping with longstanding European traditions of cathedral design. The plan unites two distinct elements: a longitudinal axis and a domed space.

Latrobe originally planned a masonry dome with a lantern on top, but his friend Thomas Jefferson suggested a wooden double-shell dome[11] (of a type pioneered by French master builder Philibert Delorme) with 24 half-visible skylights. For the inner dome Latrobe created a solid, classically detailed masonry hemisphere. Grids of plaster rosettes adorn its coffered ceiling.

The interior is occupied by a massive dome at the crossing of the Latin cross plan, creating a centralizing effect which contrasts the exterior impression of a linear or oblong building. Surrounding the main dome is a sophisticated system of barrel vaults and shallow, saucer-like secondary domes.
The light-filled interior designed by Latrobe was striking in contrast to the dark, cavernous recesses of traditional Gothic cathedrals.

A 32-month, $34 million restoration project was completed in 2006. The restoration included a total incorporation of modern systems throughout the building, while also restoring the interior to Latrobe's original design. Many "misguided accretions" were corrected.[9] The original wall colors (pale yellow, blue, and rose) were restored, as was the light-colored marble flooring which for decades had been a dark green color. Twenty-four skylights in the main dome were re-opened, and the stained glass windows (installed in the 1940s) were given to St. Louis parish in Clarksville (whose new church was designed around them) and replaced with clear glass windows.[12][13]

Additionally, the Basilica's crypt was made accessible to the public, as well as the expansive masonry undercroft (basement) of the church. The undercroft, until 2006, had been filled with sand from the original building of the cathedral, which prevented Carroll and Latrobe's vision of a Chapel in the undercroft. During the restoration, the tons of sand were removed, and the Our Lady Seat of Wisdom Chapel was finally realized.

Cardinal William Keeler, then Archbishop of Baltimore, and one of the many champions of the restoration project, completed the restoration without dipping into the coffers of the Archdiocese, instead using private funds donated for the sole purpose of the restoration. The Basilica was closed to the public from November 2004 through November 2006, reopening in time for the Basilica's Bicentennial and the biannual meeting of the United States Conference of Catholic Bishops, which was held in Baltimore to mark the occasion.

2011 Earthquake

On Aug, 23, 2011, an earthquake that jolted the East Coast from Georgia to Quebec rattled through the Basilica, sending nearly 1,000 linear feet of cracks through its ceilings and walls. A seven-month, $3 million restoration was completed on Easter Sunday 2012.[14]

Nine of the fourteen deceased Archbishops of Baltimore have been laid to rest in the Basilica's historic crypt. The crypt is located beneath the main altar, next to the Our Lady Seat of Wisdom Chapel, and is accessible to the public. Resting in the crypt are:

John Carroll, S.J., first Bishop of the United States. Served as Archbishop of Baltimore from November 6, 1789 until December 3, 1815.

Ambrose Maréchal, S.S., third Archbishop of Baltimore. Served as Archbishop of Baltimore from July 4, 1817 until January 29, 1828.

James Whitfield, fourth Archbishop of Baltimore. Served as Archbishop of Baltimore from January 29, 1828 until October 19, 1834.

Samuel Eccleston, P.S.S., fifth Archbishop of Baltimore. Served as Archbishop of Baltimore from October 19, 1834 until April 22, 1851.

Francis Patrick Kenrick, sixth Archbishop of Baltimore. Served as Archbishop of Baltimore from August 19, 1851 until July 8, 1863.

Martin John Spalding, seventh Archbishop of Baltimore. Served as Archbishop of Baltimore from May 6, 1864 until February 7, 1872.

James Cardinal Gibbons, ninth Archbishop of Baltimore. Served as Archbishop of Baltimore from October 3, 1877 until March 24, 1921.